The invention is applicable where the Time Division Multiplexing technique (TDM) is used on the site and a packet based protocol, i.e. the Internet Protocol (IP), is implemented in the transport network between the sites. Traditionally TDM (Time Division Multiplexing) traffic is today transmitted directly over SDH (Synchronous Digital Hierarchy) networks. However, it is assumed that tomorrow's telecom transport network will be packet based, but probably with a long reuse time of existing site equipment.
Many vendors believe that the future network protocol will be the Internet Protocol (IP). With the introduction of this network technology for real-time applications, telecom companies may get a dilemma. On one hand they want to adapt to the new technology, on the other hand they have a lot of equipment like MSC (Mobile Switching Centre); BSC (Base Station Controller) etc. working very well with circuit switched technology. Buying a complete new packet based solution right away and to phase out circuit switched equipment will be very expensive. Another possibility is to maintain circuit switched and packed switched networks in parallel, but this may also be regarded as too expensive. Facing the fact that the operator on long term probably will implement packet-based transport solutions anyway, i.e. the Internet Protocol (IP), a wanted solution is a mechanism that allows the Telecom Company to use today's equipment such as MSCs, BSCs etc. towards a packet switched network as an intermediate solution. Then in a later step, when the packet based technology is considered mature for real time applications on site, the change to an “all packet switched” scenario could be regarded reasonable. A problem when transporting TDM over packet based networks is the bandwidth utilization in the transport network. With Time Division Multiplexing, the connections are separated in timeslots. Depending on the traffic load situation, there will be a variable numbers of timeslots not carrying any traffic (they are IDLE). Even though there are timeslots not carrying traffic, these timeslots are today filled with a so-called “Idle Pattern”, “Idle pattern” is a fixed bit pattern and it is used in synchronous systems where there can not be any “holes” in the data stream, and transmitted through the network.
A draft to the Internet Engineering Task Force (IETF) describing the concept TDM over IP has been posted. (TDM over IP, Yaakov (Jonathan) Stein et al. March 2003) In this draft there is also a suggestion as to what the protocol stack could look like. The mentioned drafts have no option for dynamic IP bandwidth reduction. There are methods for transporting parts of a trunk (24/32 timeslots), but in a more static way. The described method is rather complicated, introducing a lot of extra overhead etc.
This invention describes a solution to avoid the transmission of the timeslots carrying Idle Pattern and hence reducing the average size of IP packets transmitted. The IP bandwidth reduction requires that information is being sent from the transmitting party to the receiving party, about which timeslots are, at a given moment, not carrying traffic. Equipment existing today provides information about whether a timeslot contains traffic or not.
The present invention uses this information to avoid transmitting timeslots not carrying traffic.
The invention introduces a method for reducing the total amount of data transmitted in a system where traditional TDM circuit switched data are transported over a packet switched network. This will bring a better utilization of the network resources.